Useful tidbit
I know this thread is really old, but I used it recently and I have figured out something useful which I wanted to share.
I had a HELL of a time getting the new belt on. I bought a GoodYear GatorBack belt, and checking the old one against the new one, the GY belt was about 1/8" shorter. Maybe that was just due to stretching of the old belt (62k miles on it). However, the new belt was impossible to get on in the manner described in all of the previous posts.
I used the "double wrench" method, but rigged a couple of small C-clamps to hold it in the un-tensioned position so that I could deal with routing the belt with both hands. I had everything routed perfectly, with only the alternator pulley remaining. It WOULD NOT go on. There was not enough slack. Yes, the tensioner was fully disengaged (it was bottoming out against the body of the tensioner mount, and would not rotate any further).
What I had to do to get the belt on finally was to have a friend rotate the crank whilst I pushed against the side of the belt to get it to slowly wind onto the alternator pulley. When I released the tensioner, the belt barely moved...
So, my guess is that since other people on here have complained about the GatorBack belts not fitting, GY made them a little small and certain individual cars require that slightly longer length that the OEM belt gives you.
Hope this is useful for someone.